Many proposals have been made for a solid catalyst component for polymerization of olefins comprising magnesium, titanium, an electron donor compound and a halogen as essential components, a catalyst for polymerization of olefins comprising said solid catalyst component, an organic aluminum compound, an organic silicon compound, etc., and a process for the polymerization of olefins which comprises polymerizing or copolymerizing olefins in the presence of said catalyst.
For example, JP-A-63-3010 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") proposes a catalyst for polymerization of olefins comprising a solid catalyst component prepared by a process which comprises allowing a dialkoxymagnesium, a diester of aromatic dicarboxylic acid, an aromatic hydrocarbon and a titanium halide to come in contact with one another, and then subjecting the product to heat treatment in powder form, an organic aluminum compound and an organic silicon compound, and a process for the polymerization of olefins.
Further, JP-A-1-315406 proposes a catalyst for polymerization of olefins comprising a solid catalyst component prepared by a process which comprises allowing a suspension of diethoxymagnesium in an alkylbenzene to come in contact with titanium tetrachloride, adding phthaloyl dichloride to the suspension for reaction to obtain a solid product, and then allowing the solid product to come in contact with titanium tetrachloride in the presence of an alkylbenzene, an organic aluminum compound and an organic silicon compound, and a process for the polymerization of olefins in the presence of said catalyst.
The foregoing various conventional techniques focus on the development of a catalyst component which is active enough to allow the omission of a so-called deashing step, i.e., step of removing catalyst residues such as chlorine and titanium remaining in the polymer produced as well as on the enhancement of the yield of stereoregular polymer and the maintenance of the catalytic activity during polymerization. These techniques can provide excellent results on these purposes. However, if a polymerization catalyst having a composition comprising this kind of a high activity type catalyst component, an organic aluminum compound and an electron donor compound such as a silicon compound is employed to polymerize olefins, the polymer thus produced contains much fine powder derived from fine solid catalyst component itself or obtained by fragmentation due to reaction heat developed during polymerization. Thus, the polymer tends to have a broad particle size distribution. If the content of the fine particle size polymer is raised, it causes the inhibition of the process. For example, the continuance of uniform reaction can be inhibited. Further, the pipe in the polymerization process can be blocked during the transfer of the polymer. In addition, if the particle size distribution is widened, it eventually gives undesirable effects on the molding of the polymer. This is the reason why a polymer having as small fine particle size polymer content as possible, a uniform particle size and a narrow particle size distribution has been desired.
In order to solve these problems, many methods have been proposed. For example, JP-A-6-157659 proposes a catalyst for polymerization of olefins made of a solid catalyst component obtained by a process which comprises adding a suspension of a spherical particulate dialkoxymagnesium, an aromatic hydrocarbon and a diester of phthalic acid to a mixed solution of an aromatic hydrocarbon and titanium tetrachloride so that they are reacted, and then reacting the reaction product with titanium tetrachloride.
For example, JP-A-6-287225 proposes a solid catalyst component for polymerization of olefins obtained by a process which comprises adding a suspension of a spherical particulate dialkoxymagnesium, an aromatic hydrocarbon and a diester of phthalic acid to a mixed solution of an aromatic hydrocarbon and titanium tetrachloride so that they are reacted, washing the reaction product with an aromatic hydrocarbon, and then again reacting the reaction product with titanium tetrachloride to obtain a solid component which is then dried and freed of fine powder.
Further, JP-A-6-287217 proposes a solid catalyst component for polymerization of olefins obtained by a process which comprises adding a suspension of a spherical particulate dialkoxymagnesium, an aromatic hydrocarbon and a diester of phthalic acid to a mixed solution of an aromatic hydrocarbon and titanium tetrachloride so that they are reacted, washing the reaction product with an aromatic hydrocarbon, again reacting the reaction product with titanium tetrachloride, drying the solid component thus obtained, removing fine powder from the solid component, and then adding a powdered nonionic surfactant to the solid component.
The foregoing technique can remove the fine powder derived from the solid catalyst component itself, eventually exerting an effect of reducing the content of fine powder in the polymer thus produced. However, the effect of the foregoing technique does not go so far as to control the generation of fine powder due to fragmentation of particles by the reaction heat developed during polymerization. Thus, a fine powder is still present in the polymer thus produced. Further, the polymer produced according to the foregoing techniques is nearly spherical and has a good morphology but has a low bulk density. In the production of a polyolefin, the amount of a polymer to be produced per unit volume in the polymerization tank is reduced, and the amount of the polymer to be processed during transportation or pelletizing step is limited. As a result, such a problem that the productivity throughout the entire process for the production of polyolefin is reduced is left unsolved.
On the other hand, a process for the production of a block copolymer of propylene has been known which comprises producing a crystalline polymer of propylene alone in the presence of a solid catalyst component or catalyst of the various conventional types at a first stage, and then copolymerizing propylene with another olefin such as ethylene and 1-butene in the copresence of said propylene homopolymer at a second stage. Such a block copolymer contains a rubber-like copolymer in a certain proportion in the composition and thus exhibits an enhanced impact strength while maintaining an excellent rigidity characteristic of crystalline polypropylene. Therefore, such a block copolymer has found wide application, e.g., to container, automobile parts such as bumper, household appliance, furniture.
In order to further enhance the impact strength of such a block copolymer, the proportion of a rubber-like copolymer (e.g., ethylene-propylene rubber) to be produced in the block copolymer needs to be raised. However, as the production ratio of rubber-like copolymer increases, the stickiness of the particulate block copolymer thus produced increases. As a result, the flowability of the particulate polymer thus produced shows a remarkable deterioration in the gas phase polymerization process or bulk polymerization process. Further, the polymer particles stick to each other to agglomerate or stick to the inner wall of the polymerization apparatus, causing serious troubles in the process operation.
For the purpose of eliminating these difficulties, JP-A-61-69821 and JP-A-61-69822 propose the supply of an active hydrogen compound such as ethanol or an oxygen-containing compound such as oxygen gas into the polymerization system at the second stage, i.e., stage of producing a rubber-like copolymer. However, such an active hydrogen compound or oxygen-containing compound originally causes deterioration of the activity of the catalyst in the polymerization of olefins. In this process, the amount of such an active hydrogen compound or oxygen-containing compound to be supplied needs to be closely controlled. Further, the apparatus to be used for this process needs to be improved.
The inventors made studies of the solution to the foregoing problems of the prior art techniques. As a result, it was found that these problems can be effectively solved by the polymerization or copolymerization of olefins in the presence of a solid catalyst component prepared from a dialkoxymagnesium having a bulk density of at least a predetermined value, or a catalyst comprising the solid catalyst component, a specific organic silicon compound and a specific organic aluminum compound. Thus, the present invention has been worked out.
It is therefore an object of the present invention to provide a solid catalyst component and catalyst for polymerization of olefins which can provide a polymer having a high bulk density and a small content of fine powder while maintaining the desired high polymerization activity and high yield of a high stereoregularity polymer. It is another object of the present invention to provide a solid catalyst component and catalyst for polymerization of olefins which can maintain its good particle properties even if the production ratio of rubber-like copolymer is raised in block copolymerization.